1. Field of the Invention
The present invention relates to a crankshaft holding structure for use in an internal combustion engine, and more particularly to a crankshaft holding structure for absorbing axial elongation and deformation of a crankshaft.
2. Description of the Background Art
Crankshafts of internal combustion engines suffer from axial elongation and deformation due to thermal expansion. However, there are crankshaft holding structures for absorbing axial elongation and deformation of a crankshaft. For example, one crankshaft holding structure is shown in Japanese Patent Laid-open No. 60-179597 entitled xe2x80x9cCrankshaft Holding Structure for Internal Combustion Engine.xe2x80x9d
This type of crankshaft holding structure includes a resilient member which is placed in a gap between an end face of a bearing and a crankcase. When a crankshaft is installed in the crankcase with bearings, the resilient member serves to absorb axial elongation and deformation of the crankshaft.
However, the resilient member required in this type of arrangement to absorb axial elongation and deformation of the crankshaft presents an obstacle to any efforts to cut down the cost of the crankshaft holding structure.
There is also a technique in the background art for absorbing axial elongation and deformation of a crankshaft without the use of a resilient member. Such a technique will be described below with reference to FIG. 4 and FIG. 5.
FIG. 4 of the accompanying drawings is a cross-sectional view of a conventional crankshaft holding structure for use in an internal combustion engine. In FIG. 4, the terms xe2x80x9cfrontxe2x80x9d and xe2x80x9crearxe2x80x9d are used to indicate front and rear sides of the holding structure.
A crankshaft holding structure 60 for use in an internal combustion engine has a rear bushing 65 of cast iron that is cast in a rear wall 62 (shown in the rear side in FIG. 4) of a crankcase 61. A radial ball bearing 70 has an outer race 71 press-fitted in the rear bushing 65 and an inner race 72 with a rear crankshaft 76 interference-fitted therein.
The crankshaft holding structure 60 also has a front bushing 66 of cast iron that is cast in a front wall 63 (shown in the front side in FIG. 4) of the crankcase 61. A radial roller bearing 73 has an outer race 74 press-fitted in the front bushing 66 and an inner race 75 with a front crankshaft 77 clearance-fitted therein. A connecting rod 79 is coupled by a connecting rod pin 78 to a counterweight 76a of the rear crankshaft 76 and a counterweight 77a of the front crankshaft 77.
Since the front crankshaft 77 is clearance-fitted in the inner race 75 of the radial roller bearing 73, axial elongation and deformation of the crankshafts 76, 77 can be accomodated in the direction toward the radial roller bearing 73 as indicated by the arrow xe2x80x9ca.xe2x80x9d
FIG. 5 of the accompanying drawings is an enlarged view of an encircled area 5 shown in FIG. 4. The counterweight 77a of the front crankshaft 77 has a land 77b confronting the front bushing 66 and spaced from an end face 66a thereof by a gap L5. The gap L5 is set to a value smaller than a gap L6 between an inner side surface 75a of the inner race 75 and a stepped wall surface 77c of the counterweight 77a. 
When the elongation or deformation of the rear crankshaft 76 and the front crankshaft 77 increases, the land 77b abuts against the end face 66a of the front bushing 66 before the stepped wall surface 77c of the counterweight 77 abuts against the inner race 75 of the radial roller bearing 73. This limits crankshaft elongation and deformation due to thermal expansion of the crankshafts.
Therefore, since no axial load is applied to the inner race 75 of the radial roller bearing 73, rollers 73a of the radial roller bearing 73, for example, are prevented from being locally worn.
In order to make the gap L5 between the land 77b and the end face 66a of the front bushing 66 smaller than the gap L6, it is necessary that the front bushing 66 projects from the front wall 63 of the crankcase. Since the front bushing 66 thus projecting from the front wall 63 has an increased width W5, the front bushing 66 has a relatively larger shape.
In addition, in order to keep the land 77b in uniform abutment against the end face 66a of the front bushing 66, the end face 66a of the front bushing 66 needs to be machined in its entirety to a flat surface. However, it is time-consuming to machine the end face 66a as it is normally annular in shape. Therefore, the machining process inhibits attempts to further reduce the cost of the front bushing 66 and the crankshaft holding structure.
Furthermore, in order to satisfy the dimension of the gap L5, the extent to which the end face 66a of the front bushing 66 projects needs to fall within an allowable range. However, since the front bushing 66 is cast in the front wall 63 of the crankcase 61, dimensional errors tend to be large.
It is tedious and time-consuming to manage gap dimensions so as to keep the extent of projection of the front bushing 66 within this allowable range. The tedious and time-consuming process of dimensional management also obstructs efforts to minimize the cost of the structure.
As much as the front bushing 66 projects from the front wall 63 of the crankcase, the width W5 of the front bushing 66 is correspondingly larger. Therefore, this increase in size of the front brushing 66 virtually eliminates the ability to use the front bushing 66 and the rear bushing 65 (see FIG. 4) as common parts, e.g. interchangeably. Accordingly, it becomes necessary to manage and store different types of bushings. However, there is a demand for using the front and rear bushings as common parts that is further complicated by the aforementioned arrangement of the background art.
The present invention overcomes the shortcomings associated with the background art and achieves other advantages not realized by the background art.
It is an aspect of the present invention to provide a crankshaft holding structure for use in an internal combustion engine that includes a simplified structure.
It is an aspect of the present invention to provide a crankshaft holding structure having bushings with bearings press-fitted therein.
It is an additional aspect of the present invention to provide a crankshaft holding structure permitting bushings to be used as common parts.
These and other aspects of the present invention are accomplished by a crankshaft holding structure for an internal combustion engine, the crankshaft holding structure comprising a crankcase; a plurality of bearings including at least one radial roller bearing having an outer race, the outer race fixed to the crankcase; and a crankshaft having a side surface, the side surface of the crankshaft abutting against a side surface of the outer race of the radial roller bearing and limiting an axial elongation and a deformation of the crankshaft.
The outer face of the radial roller bearing is mounted on the crankcase so as not to be axially displaced when the side surface of the crankshaft abuts against the outer face of the radial roller bearing. In view of this arrangement, the side surface of the crankshaft is held in abutment against the side surface of the outer race of the radial roller bearing for thereby limiting axial elongation and deformation of the crankshaft. Since the outer race of the radial roller bearing is not axially displaced, rollers of the radial roller bearing are prevented from becoming locally worn.
The side surface of the outer race of the radial roller bearing against which the side surface of the crankshaft abuts is machined to a flat finish in advance. Therefore, any process of subsequently machining the side surface of the outer race to a flat finish can be dispensed with. In addition, because the radial roller bearing is press-fitted in the crankcase while being positioned highly accurately, the management of the dimensions of the side surface of the outer race is simplified.
Furthermore, since the side surface of the crankshaft is held in abutment against the side surface of the outer race of the radial roller bearing, it is not necessary to hold the side surface of the crankshaft in abutment against an end face of a bushing in which the radial roller bearing would be press-fitted, as is the case with the conventional structure. Consequently, it is not necessary to project the end face of such a bushing and machine the projecting end face to a flat finish.
These and other aspects of the present invention are accomplished by a crankshaft holding structure for an internal combustion engine, the crankshaft holding structure comprising a crankcase; a plurality of bushings having respective inner diameters, wherein the inner diameters of the bushings are equal; a plurality of bearings including at least one radial roller bearing having an outer race, the outer race press-fitted within a first bushing fixed to the crankcase; and a crankshaft having a first side surface and second side surface, the first side surface of the crankshaft abutting against a side surface of the outer race of the radial roller bearing and limiting an axial elongation and a deformation of the crankshaft.
When the outside diameters of the bearings are identical to the outside diameter of the radial roller bearing, bushings in which the bearings are press-fitted have the same diameters. Therefore, the front and rear bushings can be used as common parts.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.